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Ames Laboratory

Astrophysics and Astronomy

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Articles 1 - 6 of 6

Full-Text Articles in Physics

Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel Jan 2015

Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Sulfur-metal complexes, containing only a few atoms, can open new, highly efficient pathways for transport of metal atoms on surfaces. For example, they can accelerate changes in the shape and size of morphological features, such as two-dimensional nanoclusters, over time. In this study we perform STM under conditions that are designed to specifically isolate such complexes. We find a new, unexpected S-Cu complex on the Cu(111) surface, which we identify as Cu2S3. We propose that Cu2S3 enhances mass transport in this system, which contradicts a previous proposal based on Cu3S3 ...


Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their ...


Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides Dec 2014

Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging “explosively” out of the compressed wetting layer after a critical coverage Θc ¼ 1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result ...


Search For The Structure Of A Sulfur-Induced Reconstruction On Cu(111), Da-Jiang Liu, Holly L. Walen, Junepyo Oh, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2014

Search For The Structure Of A Sulfur-Induced Reconstruction On Cu(111), Da-Jiang Liu, Holly L. Walen, Junepyo Oh, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

We have carried out an extensive DFT-based search for the structure of the (√43 × √43)R ± 7.5° reconstruction of S on Cu(111), which exhibits a honeycombtype structure in scanning tunneling microscopy (STM). We apply two criteria in this search: The structure must have a reasonably low chemical potential, and it must provide a good match with STM data, both our own and the data published by Wahlström et al. Phys. Rev. B 1999, 60, 10699. The best model has 12 S adatoms and 9 Cu adatoms per unit cell. Local defects within the Cu9S12 framework, consisting of ...


Analytic Formulations For One-Dimensional Decay Of Rectangular Homoepitaxial Islands During Coarsening On Anisotropic Fcc (110) Surfaces, Chi-Jen Wang, Yong Han, Holly L. Walen, Selena M. Russell, Patricia A. Thiel, James W. Evans Jan 2013

Analytic Formulations For One-Dimensional Decay Of Rectangular Homoepitaxial Islands During Coarsening On Anisotropic Fcc (110) Surfaces, Chi-Jen Wang, Yong Han, Holly L. Walen, Selena M. Russell, Patricia A. Thiel, James W. Evans

Chemistry Publications

Submonolayer homoepitaxial fcc (110) systems display behavior reflecting strong anisotropy at lower temperatures, including one-dimensional decay during Ostwald ripening of rectangular islands maintaining constant width in the 〈001〉 direction. To appropriately describe this behavior, we first develop a refined continuum Burton-Cabrera-Frank formalism, which accounts for a lack of equilibration of island shape and importantly also for inhibited incorporation of adatoms at almost-faceted 〈1̄10〉 island edges through effective kinetic coefficients. This formalism is shown to describe accurately the adatom diffusion fluxes between islands and thus island evolution for a complex experimental island configuration, as confirmed by matching results ...


Far-From-Equilibrium Film Growth On Alloy Surfaces: Ni And Al On Nial(110), Yong Han, Dapeng Jing, Baris Unal, Patricia A. Thiel, James W. Evans Jan 2011

Far-From-Equilibrium Film Growth On Alloy Surfaces: Ni And Al On Nial(110), Yong Han, Dapeng Jing, Baris Unal, Patricia A. Thiel, James W. Evans

Chemistry Publications

STM analysis reveals diverse nonequilibrium island structures formed by deposition of Ni and Al on NiAl(110) at around 300 K. Epitaxial growth in this complex alloy system is described by multisite lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This approach accounts for multiple adsorption sites and diffusion paths, and accurately describes diffusion and detachment kinetics for a vast number of step-edge configurations. This is key for realistic description of island growth shapes, structure, and partial alloy ordering.